RF simplex spread spectrum receiver and method with symbol deinterleaving prior to bit estimating

#This invention relates to a method and system for improving the bit error rate performance of a receiver in a spread spectrum radio frequency (RF) communication system with orthogonal digital signals and biorthogonal modulation in the presence of RF channel impairments, for example, additive white Gaussian noise. More particularly, this invention relates to the reception of a biorthogonally modulated spread spectrum digital signal by means of a multiple-step demodulator and error correction code (ECC) decoder which reduces the probability of error for some fraction of the received bits

#A portion of the disclosure of this patent application contains material which is subject to copyright protection. The copyright owner has no objection to the reproduction by anyone of the patent document as it appears in the Patent and Trademark Office files or records, but otherwise reserves all copyrights whatsoever. Software for carrying out some of the methods and systems described herein has been filed with the United States Patent and Trademark Office herewith in the form of a microfiche appendix including numerous frames, one of which being a title frame. The microfiche appendix is entitled RF SIMPLEX SPREAD SPECTRUM RECEIVER AND METHOD WITH SYMBOL DEINTERLEAVING PRIOR TO BIT ESTIMATING and includes one (1) microfiche and seventy-four (74) frames.

#Robust mobile digital communication is difficult to accomplish because of the deleterious effects of the environment on the propagation characteristics of the radio-frequency (RF) channel (from about 0 to 100 Gigahertz). Atmospheric conditions and variations in terrain, foliage, and the distribution and density of man-made structures and operating machinery strongly affect the characteristics of the medium which RF signals traverse. Satellite communication systems are typically limited by insufficient electromagnetic radio-frequency (RF) field strength due to the presence of background cosmic, atmospheric, and man-made noise which together establish an irreducible noise floor. Satellite systems may also be limited by the thermal noise of the active electronic components used in the implementation of the receiver system. Terrestrial mobile communications systems are also subject to performance degradation due to the effects of background and thermal noise. However, terrestrial mobile receiver systems are further degraded by multipath propagation due to the reception of signals corresponding to paths other than the line-of-sight (LOS) propagation path.

#FIG. 1 is a block diagram of a prior art biorthogonal receiver.

#FIG. 2 is a block diagram of a prior art method of biorthogonal demodulation in the FIG. 1 receiver.

#FIG. 3 is a graph illustrating an exemplary distribution of the correlation sums at the sampling point in the determination of the selection bit in the FIG. 2 prior art biorthogonal demodulator when the RF impairment is additive white Gaussian noise (AWGN).

#Referring now more particularly to the accompanying drawings in which like reference numerals indicate like parts throughout the several views.

#FIG. 5 is a block diagram of the biorthogonal receiver system according to the invention. The functions of the RF-tuner 1, ADC 3, baud clock recovery 5, carrier frequency recovery 7, equalizer 9, and descrambler 17 in the biorthogonal receiver system are as in the prior art biorthogonal receiver of FIG. 1. The prior art biorthogonal demodulator 11 in FIG. 1 is replaced with the biorthogonal demodulator of the invention 69 in FIG. 5, which is shown in further detail in FIG. 6 for the specific embodiment where M is two (2). Deinterleaver 13 in FIG. 1 is replaced with symbol deinterleaver 71 with a specific internal structure. The prior art ECC decoder 15 in FIG. 1 is replaced with multiple-step ECC decoder 73 (see FIG. 5), which is shown in detail in FIG. 7.

#In general, there are two types of interleavers that may be implemented in a communication system, (i) "bit" interleavers and (ii) "symbol" interleavers in the transmitter system with corresponding bit and symbol deinterleavers in the receiver. The difference between bit interleaving and symbol deinterleaving is that, in a symbol interleaver, while the ordering of groups of bits are shuffled so as to eliminate probable temporal correlation between adjacent groups, the bit ordering within each group of bits is preserved by the shuffling process. In a bit interleaver, no specific ordering among adjacent bits is preserved. According to the method, symbol deinterleaving is required in the receiver system of this invention, and consequently symbol interleaving is used in the transmitter in order to preserve the association between the selection and polarity bits in each baud.